In this piece, I focus on Brazil, and in particular, the country’s socio-economic context, public health infrastructure, and its experience of the Zika virus epidemic to date. Brazil is geographically very diverse, has a strong economy, and also huge inequalities. The country has undergone epidemiological and demographic transition with infectious disease mortality dropping from 50% to 5% in the past 80 years, although many issues with infectious disease remain. The central unified health system was created in 1988 and established a hierarchical disease surveillance and response model. Previously, all aspects of endemic disease control, including fumigation, insect control, and laboratory work were managed centrally. Since the 1990s, this responsibility has been devolved to the municipalities and there have been consequences as a result of this shift.

Brazil’s has a universal surveillance system that involves notification and laboratory testing, in the case of meningitis for example, with different approaches for difference diseases. For vector-borne diseases, like yellow fever and dengue, surveillance cannot be restricted to notification of cases. Port, airport and zoonotic surveillance are all necessary, involving a network of laboratories and of notification that’s quite complex and challenging for a low or middle-income country. However, Brazil’s surveillance system is strong if compared to other low and middle-income countries.

Turning to Zika, the virus has an Asian and African lineage, with the outbreak in the Americas linked to the Asian one. It is closely related to the dengue, yellow fever, West Nile, and Japanese encephalitis viruses. Zika is an arbovirus of the flaviviridae family and is spread by mosquitoes of the Aedes genus. Arboviruses are very particular and have preferences for which mosquito they like to be carried by. The mosquito of the genus Aedes can also carry dengue, and chikungunya. Brazil has had a rampant dengue epidemic since the 1980s. The incubation period of Zika in humans is estimated as being five to seven days, although the evidence is inconclusive. And of course, we have mainly monkeys and humans as hosts. Virus detection and confirmation require polymerase chain reaction (PCR) test, virus isolation by culture, or using an ELISA test for antibodies.

The Zika virus causes mild symptoms compared with dengue. Patients present with a maculopapular rash, a very low-fever, malaise, and some conjunctivitis. Itchiness can be more intense than in cases of dengue or chikungunya. Importantly, the Zika virus is neurotropic; it likes the nervous system and can cause Guillain-Barré syndrome and also microcephaly, the latter of which if transmitted from mother to child in utero.

Zika was first discovered in Uganda in 1947 and until the mid-2000s, had never left the Asian or African continent. Then, in 2007, there was a modest outbreak in the Yap Islands, Micronesia. In 2013-14 a bigger outbreak in French Polynesia was reported, and it is possible that Zika could have reached the Americas via the Easter Islands off the coast of Chile in 2014. It then reached Brazil in 2015. There is a plausible hypothesis that the influx of high numbers of foreigners during the 2014 World Cup, including from the Easter Islands and other Pacific islands where Zika had been circulating, might have contributed to the Brazilian outbreak. Furthermore, Aedes mosquito is also very prevalent in Brazil and, previous to Zika, an outbreak of chikungunya in the same area (Bahia) had been described. It is not surprising that the Zika virus then took off. Nine months later, medical professionals in the state of Pernambuco reported an increase in the number of newborns with microcephaly, using the Brazilian system of newborn notification. It is my hypothesis that surveillance of infectious disease alone without a strong system for collecting demographic and health information is an impoverished approach. The existence of the newborn notification system was the primary reason why Brazil was the first country to detect instances of microcephaly. Only after Brazil notified the WHO of the increase of microcephaly in newborns and the potential relationship with Zika did French Polynesia start examining its cases.

Therefore, temporal-spatial distribution is one method by which people are drawing the epidemiological relationship between microcephaly and the Zika virus. There is also geographical overlap between the two, i.e. instances of Zika fever and then microcephaly cases approximately 9 months later in the same municipalities. Further analysis of the data demonstrated that the period of high Zika circulation coincided with the first trimester of pregnancy amongst the mothers of affected babies. Analysis of the medical records of around 60 mothers corroborated the findings. The increased number and pattern of distribution of microcephaly cases were also compatible with the locations where Zika was circulating. Similarly, the fact that Zika is a neurotropic virus (seen in animal models) increases the likelihood of association between the two conditions. Further support came when French Polynesia subsequently reported cases of Zika-induced microcephaly to the WHO. Since then, there has been isolation of the virus or its proteins in some cases of sick or aborted babies with microcephaly.

Luciana Brondi is a physician, epidemiologist, and infectious disease specialist who has previously worked with the Brazilian Ministry of Health.